The present invention relates generally to the field of cellular communication systems, and, more particularly, to cellular communication systems that use time division multiple access (TDMA) technology, such as those based on the Telecommunication Industry Association (TIA)/Electronic Industries Association (EIA)/American National Standards Institute (ANSI) 136 standard or the global system for mobile communication (GSM) standard.
Wireless communications systems are commonly used to provide voice and data communications to subscribers. For example, analog cellular radiotelephone systems have long been deployed successfully throughout the world. Digital cellular radiotelephone systems, such as those conforming to the North American TIA interim standard (IS) 54 and the European standard GSM have been in service since the early 1990's. More recently, a wide variety of wireless digital services have been introduced, which are broadly labeled as PCS (Personal Communications Services), and include advanced digital cellular systems conforming to standards such as ANSI-136 and IS-95, lower-power systems such as DECT (Digital Enhanced Cordless Telephone), and data communications services such as CDPD (Cellular Digital Packet Data). These and other systems are described in The Mobile Communications Handbook, edited by Gibson and published by CRC Press (1996).
FIG. 1 is a high-level block diagram of a conventional GSM network 20. The GSM network includes a base station subsystem 22 that communicates with a mobile terminal 24 using a radio link protocol. The base station subsystem 22 may also communicate with a Serving Generalized Packet Radio Service (GPRS) Support Node (SGSN) 26 and a Mobile Switching Center (MSC) 28. The SGSN 26 may access an external packet data network 32 via a Gateway GPRS Support Node (GGSN) 34. The MSC 28 typically functions as a conventional switching node in the Public Switched Telephone network (PSTN)/Integrated Services Data Network (ISDN) 36. The SGSN 26 and the MSC 28 may be coupled to each other and may also access a pair of databases known as the Home Location Register (HLR) 38 and the Visitor Location Register (VLR) 42.
The base station subsystem 22 may comprise a base station controller and one or more base transceiver stations. A base transceiver station contains the radio transceiver that defines an individual cell in the GSM network and communicates with mobile terminals in the cell using a radio-link protocol. The base station controller is generally used to manage resources for one or more base station transceivers. These resource management duties may include radio-channel setup, frequency hopping, and hand-offs of mobile terminals between cells.
GSM provides both circuit switched data services and packet switched data services. Packet switched data services are provided through a GSM protocol known as GPRS. The base station subsystem 22 may communicate with the SGSN 26 for packet switched and/or circuit switched data connections. Conversely, the base station subsystem 22 may communicate with the MSC 28 for voice connections.
The MSC 28 and the SGSN 26 may provide the functionality used to service the mobile terminal 24 along with other mobile terminals in the GSM network. In particular, the MSC 28 and SGSN 26 may provide registration, authentication, location updating, hand-offs, and call routing services to roaming subscribers. To provide these services, the MSC 28 and SGSN 26 may access information stored in the HLR 38 and the VLR 42 databases.
For example, the HLR 38 typically contains administrative information associated with subscriber's registered in the GSM network along with the current locations of the subscribers' mobile terminals. The location of a mobile terminal may be represented as the signaling address of the VLR 42 associated with the mobile terminal. The VLR 42 typically contains selected administrative information from the HLR 38 for mobile terminals that are currently located in the geographical region controlled by the VLR 42. Accordingly, the MSC 28, SGSN 26, HLR 38, and VLR 42 may cooperate to provide call routing and roaming functionality for the GSM network.
As end-user services move towards mobile multimedia, a new technology, known as Enhanced Data Rates for Global Evolution (EDGE), may be used in GSM networks to boost network capacity and increase data rates. EDGE may increase data rates for circuit switched connections via an Enhanced Circuit Switched Data (ECSD) mode and for packet switched connections via an Enhanced Generalized Packet Radio Service (EGPRS) mode up to three-fold. Moreover, because EDGE is built on the existing GSM standard and uses the same TDMA frame structure, EDGE service may typically be introduced into a GSM network via a software/firmware retrofit of the base station subsystem 22 and introduction of EDGE compatible mobile terminals.